This section provides background information related to the present disclosure which is not necessarily prior art.
In an attempt to reduce the quantity of NOX and particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system (including a urea injector), a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC).
Another aftertreatment device that has shown promise in reducing NOx emitted to the atmosphere is a lean NOx trap (LNT). A LNT is a device that traps the NOx (NO and NO2 molecules) in a manner similar to a sponge. Once the LNT is full (like a sponge full of water) no more NOx can be absorbed. Thus, various schemes have been designed to “purge” or “regenerate” the trap. One scheme used to purge the LNT is the injection of diesel fuel upstream of the LNT. In this regard, the diesel fuel provides hydrocarbons that, under rich conditions, chemically react with the adsorbed NOx to produce water (H2O) and nitrogen (N2) as products of the chemical reaction. The use of diesel fuel as a reactant, however, results in a fuel penalty that is undesirable. It is desirable, therefore, to develop an exhaust aftertreatment system having a LNT that does not utilize diesel fuel as a reactant to purge or regenerate the LNT.